United States Geological Survey
California Geological Survey
Under contract to
SPA Risk LLC
Ronald T. Eguchi and Shubharoop Ghosh
Long Beach, CA
The ShakeOut Scenario:
U.S. Geological Survey Open File Report 2008-1150
California Geological Survey Preliminary Report 25 version 1.0
Note: over the course of the ShakeOut Scenario, the project name
evolved. Where a study mentions the SoSAFE Scenario or San Andreas
U.S. Geological Survey Circular 1324 Fault Scenario, it refers to what is now named the ShakeOut Scenario.
California Geological Survey Special Report 207 version 1.0
Impacts of a M7.8 Southern San Andreas Fault Earthquake: A
Hazardous Materials Release Scenario
By Ronald T. Eguchi and Shubharoop Ghosh, ImageCat, Inc.
Over 175,000 people would be affected by a hazardous materials release that originates in
Los Angeles County as a result of a M7.8 earthquake on the southern San Andreas Fault.
This assessment is based on scaling the results of an earlier study by Seligson et al. (1996).
It is generally acknowledged that a major earthquake in an industrialized, densely populated
area of the U.S. could lead to the release of hazardous chemicals. A large post-earthquake
release would present a threat not only to residents in the immediate vicinity of the source,
but also to those of surrounding communities. Affected areas would then face a range of
emergency management problems. For example, a major earthquake is likely to seriously
impair community emergency response capability, making it difficult to effectively deal
with secondary emergencies such as hazardous materials releases and fires. Tasks which are
normally problematic, such as warning the public about a toxic release and evacuating
people from areas that are hazardous, would be much more difficult following a major
earthquake. Further, communities are accustomed to responding to hazardous materials
releases one at a time, while in an earthquake situation multiple accidents may occur
simultaneously, greatly compounding resource problems.
Although there has never been a major incident involving hazardous materials in a
U.S. earthquake, smaller releases have occurred in events that were moderate in size. An
example is an accident at a chlorine repackaging facility in the 1987 Whittier Narrows
Earthquake, in which nearly one ton of chlorine gas was released (FEMA, 1987). While
awareness of the problem is growing, there has been little research to date on the seismic
sources of hazardous materials releases, and seismic vulnerability models for chemical
facilities are almost nonexistent.
The main challenge in approaching this problem from a community perspective is to
develop a risk assessment methodology that is sophisticated enough to provide the type of
information needed for more effective hazard management, but is also cost-effective to
apply on a regional basis. Conducting detailed seismic risk assessments and modeling
potential failures in chemical facilities is very time consuming and expensive; few
communities can afford to conduct such studies.
Adding to the complexity of the problem, highly hazardous materials number in the
thousands and new products are constantly being developed. Before systematic analyses
can be undertaken, it is necessary to determine which hazardous substances are likely to
pose the biggest threat to the community in an earthquake. In this limited assessment, we
have chosen to focus on two hazardous materials; chlorine and ammonia. These substances
were selected because: (1) they are responsible for the majority of fatalities and casualties in
U.S. hazardous materials incidents; (2) they are present in large quantities in our study area,
Greater Los Angeles; and (3) they form clouds that can spread to adjacent areas, thus
presenting a hazard beyond the plant gates.
Because of the limited resources devoted to the current effort, we have chosen to
base our assessment on hazardous materials release scenarios which were produced several
years ago by Seligson et al. (1996) where the effects of three earthquakes in the southern
California area were evaluated. In that study, the potential impact of hazardous material
release (limited to chlorine and ammonia) on southern California populations was
determined from a M8+ earthquake on the southern San Andreas fault, a M7.0 earthquake
on the Newport-Inglewood fault, and a M5.9 earthquake on the Whittier-Elsinore fault.
This latter event involved the calibration of fragility and hazardous materials release models
using data collected after the 1987 Whittier Narrows earthquake.
The purpose of the current study was to describe the impacts of a M7.8 earthquake on the
Southern San Andreas Fault on hazardous materials handling facilities in Los Angeles
County. Because of the limited resources which were dedicated to this effort, the authors
used their judgment in scaling the results of a similar study completed by Seligson and
others in 1996. The first author of this report was the Principal Investigator for that effort.
The basis for the current approach was to scale the results of the Seligson report either
upward or downward depending on how recently released ground motion intensities by the
U.S. Geological Survey (USGS), as reported in its Multihazards Demonstration Project (see
http://pubs.usgs.gov/of/2007/1255/section4.html), compared with those ground motions
initially reported in the Seligson report. Since the measure of ground shaking intensity in
the Seligson report was Modified Mercalli Intensity (MMI), this ground motion index was
used as the basis for comparison. Furthermore, since the Seligson report only considered
hazardous materials release sources in Los Angeles County, the current assessment would
not be entirely reflective of what might occur in a San Andreas event that causes damage to
facilities in areas outside of Los Angeles County. The current scenario modeled here,
however, is still considered significant in that many hazardous materials handling facilities
are located in Los Angeles County and the populations that surround these facilities are
Description of Facilities
The group of facilities that were examined in the Seligson study included twenty-two of the
largest users of chlorine and anhydrous ammonia in the greater Los Angeles area. As part of
this current effort, the authors reviewed the list of facilities considered in the earlier study
and confirmed that each facility was still in operation.
The users include petroleum refineries, chemical manufacturers, and wastewater
treatment plants. The inventory data for these facilities were obtained from a survey
conducted by the South Coast Air Quality Management District (AQMD) in the 1990s.
Although local and state laws were in effect at that time that required all users and handlers
of hazardous chemicals to report on-site inventories, these programs were fairly new. Thus,
the AQMD data were used as the primary data for the original effort.
The facilities store and use varying amounts of chemicals, and are dispersed
throughout Los Angeles County. In general, they are broken into three facility types based
on chemical usage: chlorine storage facilities, ammonia storage facilities, and ammonia
processing facilities. Chlorine storage amounts range from 4 to 1000 tons, while ammonia
storage varies from 2 to 206 tons. Table 1 indicates the usage of each facility, and the
amount of each chemical stored on-site at the time of the original study. The reader is
referred to the Seligson report for more information on each facility including facility type.
The three earthquake scenarios that were considered in the Seligson report were:
M8+ earthquake on the southern San Andreas fault – 300 kms of rupture along the
Mojave, San Bernardino Mountain and Coachella Valley segments of the fault;
M7 earthquake on the Newport-Inglewood fault; and
M5.9 earthquake on the Whittier-Elsinore fault – a re-creation of the 1987 Whittier
Peak ground accelerations were initially calculated at each facility location using a
deterministic magnitude-distance attenuation relationship (Campbell, 1981). These peak
ground accelerations were then converted to MMI values using a conversion equation
developed by Trifunac (1976). These conversions yielded MMI values equivalent to PGA
values for sites located on "basement rock".
In order to account for variations in local ground conditions from "basement rock",
MMI modifiers were added to the "basement rock" MMI values. These modifiers were
based on Evernden and Thomson's (1985) site soil classifications and local soil information.
Data on generalized local ground conditions for the study area were derived from published
geologic maps, including maps generated by Tinsley and Fumal (1985), from their study of
the areal variations in shaking response due to earthquakes in southern California.
For the USGS Multihazard Demonstration Project, MMI values were provided by
Keith Porter at the University of Colorado at Boulder. As part of the current effort, the
locations of the 22 facilities were plotted directly onto the USGS MMI map.
Table 2 shows a comparison of the different MMIs. The comparison indicates that
the ground motions computed in the more recent USGS study are generally higher than
those produced by the Seligson report for the San Andreas event, but nearly equal to those
produced by the Seligson report for the Newport-Inglewood event. Figure 1 shows a map of
facility locations plotted on the USGS MMI map.
The impacts of hazardous materials release are expressed in terms of percent of
population exposed. Potential zones of vulnerability were established in the Seligson study
based on specific health criteria or levels of concern for both Cl2 and NH3. The chemical-
specific health criteria used were based on the Emergency Response Planning Guidelines
(ERPGs) developed by a committee of the American Industrial Hygiene Association
(AIHA). The threshold criteria used was ERPG 3, "the maximum airborne concentration
below which it is believed that nearly all individuals could be exposed for up to one hour
without experiencing or developing life-threatening health effects." This exposure level is
20 ppm for Chlorine and 1000 ppm for Ammonia. The reader is referred to the Seligson et
al. report for a description of the population exposure methodology, i.e., plume modeling
and exposure analysis.
Based on the assumption that the ground shaking intensities (MMI) for the USGS M7.8 San
Andreas earthquake are similar to those produced in the Seligson report for its M7 Newport-
Inglewood event, we conclude that the impacts from the USGS scenario will be on the same
order of magnitude as those presented by Seligson’s Newport-Inglewood scenario. Table 3
shows the results of both the Newport-Inglewood scenario and the M8+ scenario as
originally presented by the Seligson report. These are provided for reference.
Since the populations in Los Angeles and Orange Counties have grown since the
release of the Seligson et al. (1996) study, we have scaled the exposed population numbers
for those counties by factors of 1.3 and 1.6, respectively. Given this scaling, we estimate
that the total number of people that will be exposed to a hazardous materials release in a
large San Andreas event would be over 175,000. The population centers that will be most
affected will be those that are located near facilities with high intensities, i.e., facilities 5 and
8. These facilities are located near the cities of Vernon, Commerce, Maywood, Bell
Gardens and Bell.
The authors would like to thank Hope Seligson of MMI Engineering for providing data and
information on the original hazardous materials release study. The Seligson et al. (1996)
study was originally funded by the National Science Foundation (Grant No. ECE-8600292)
and the Multidisciplinary Center for Earthquake Engineering Research (Grant No.
Campbell, K.W., 1981. "A Ground Motion Model for the Central United States Based on
Near-Surface Acceleration Data," Proceedings of Earthquakes and Earthquake Engineering:
The Eastern United States, September 14-16, Knoxville, Tennessee.
Evernden, J.F. and J.M. Thomson, 1985. "Predicting Seismic Intensities," Evaluating
Earthquake Hazards in the Los Angeles Region - An Earth Science Perspective, J.I. Ziony,
ed., U.S. Geological Survey Professional Paper 1360, pp. 151 - 202.
FEMA, 1987. "The Los Angeles - Whittier Narrows Earthquake of October 1, 1987:
Federal/State Hazard Mitigation Survey Team Report," Prepared by the Federal Emergency
Management Agency, Region IX; California Governor's Office of Emergency Services,
Southern California Earthquake Preparedness Project and Planning Division, Nov. 1987.
Seligson, H.A., Eguchi, R.T., Tierney, K.J., and K. Richmond, 1996. “Chemical Hazards,
Mitigation and Preparedness in Areas of High Seismic Risk: A Methodology for Estimating
the Risk of Post-Earthquake Hazardous Materials Release,” Technical Report NCEER-96-
0013, November 7, 1996.
Tinsley, J.C. and T.E. Fumal, 1985. "Mapping Quaternary Sedimentary Deposits for Areal
Variations In Shaking Response," Evaluating Earthquake Hazards in the Los Angeles
Region - An Earth Science Perspective, J.I. Ziony ed., U.S. Geological Survey Professional
Paper 1360, pp. 101 - 125.
Trifunac, M.D., 1976. "A Note on the Range of Peak Amplitudes of Recorded
Accelerations, Velocities, and Displacements with Respect to the Modified Mercalli
Intensity Scale," Earthquake Notes, vol. 47, no. 1.
TABLE 1. Chemical Facility Use and Storage - Los Angeles County (as determined by
Seligson et al, 1996)
Facility Facility Type Chemical Storage
Chlorine Ammonia Ammonia Chlorine Ammonia
Storage Storage Processing (Tons) (Tons)
1 x x 4 40
2 x x 32 57
3 x x 8 26
4 x x 12 206
5 x 180
6 x 5
7 x x 10 15
8 x 450
9 x 5
10 x 26
11 x 454
12 x x 1000 14
13 x 25
14 x x 20 15
15 x x 270 1
16 x 90
17 x 48
18 x 26
19 x x 10 10
20 x 6
21 x x 24 2
22 x 100
Total 19 6 7 2653 Tons 538 Tons
TABLE 2. MMI Comparisons between Seligson et al. (1996) report and USGS
San Andreas Scenario Seligson et
Seligson et al. 1996 Inglewood
Facility Number Report M8.3 USGS M7.8 Scenario M7
1 8 8 9
2 7 9 9
3 7 9 9
4 8 8 9
5 8 10 9
6 8 9 10
7 7 9 9
8 8 10 9
9 8 9 8
10 8 9 8
11 7 9 9
12 8 8 9
13 8 8 9
14 8 8 9
15 8 9 8
16 8 9 9
17 8 8 9
18 8 8 7
19 7 9 9
20 8 9 9
21 7 8 9
22 8 9 8
TABLE 3. Population Exposure to Hazardous Materials by County (Seligson et al.,
County Population Total Percent
Exposed Population Exposed
Scenario 1: M 7.0 Los Angeles 132,509 7,477,503 1.800%
Newport/Inglewood Orange 491 1,932,709 0.030%
Event Riverside 0 663,166 n/a
San Bernardino 0 895,016 n/a
Ventura 0 529,174 n/a
Scenario 2: M 8.3 Los Angeles 20,546 7,477,503 0.300%
San Andreas Event Orange 217 1,932,709 0.010%
Riverside 0 663,166 n/a
San Bernardino 0 895,016 n/a
Ventura 0 529,174 n/a
Scenario 3: M 5.9 Los Angeles 6,503 7,477,503 0.090%
Whittier/Narrows Orange 157 1,932,709 0.008%
Earthquake Riverside 0 663,166 n/a
San Bernardino 0 895,016 n/a
Ventura 0 529,174 n/a
Note: Only hazardous materials sites in Los Angeles County were considered in the Seligson et al.
USGS Ground Motion Map
Figure 1. Facility Locations and MMI Values from USGS Demonstration Project.